LU-6312 lfsck: modify llsd_master_list with spin_lock

LU-6312 lfsck: modify llsd_master_list with spin_lock

There was spin_lock leak in layout LFSCK lfsck_layout_slave_quit,
that may cause modifying lfsck_layout_slave_data::llsd_master_list
without spin_lock when others traverses such list with spin_lock,
as to the later one(s) access invalid RAM or fall into soft-lockup.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I4d534313ec3f2cbdbed142cb1ee63c19404bbe65
Reviewed-on: http://review.whamcloud.com/13944
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>